1. Field of Invention
The invention relates to an apparatus and a method for producing bags comprising fabric made of stretched plastic strips as described herein.
2. Description of the Prior Art
Such apparatuses are known in the prior art and available on the market for quite a while now. These apparatuses usually first comprise a separating device in order to separate a supplied fabric tube that can additionally be laminated into tube pieces. These tube pieces comprise two material webs lying on top of each other. The tube pieces are then received by at least one transport device in order to deliver them to the individual processing stations. The individual processing stations are listed below together with an explanation of their functions.                In the pre-creasing station, form punches are lowered onto the tube piece for producing fold lines. The turned-in corners of the opened tube bottom will later be located on these fold lines. The form punches can also be heated for this purpose.        In the bottom-opening station, at least one end of a tube piece is raised so that a bottom can be molded on this raised end. The turned-in corners will later be located on the fold lines of the tube piece. Due to its geometric shape, the bottom opening is also called bottom square. It should be noted here that the shape of the bottom opening is not square, but rectangular in most cases. Both ends of a tube piece are usually processed in a similar manner.        In the valve patch station, a valve patch is applied to the previously opened bottom of the tube piece. The valve patch enables the finished bag to be filled later by means of a suitable fill nozzle.        In a so-called closing station, parts of the bottom openings or the bottom squares, the so-called tabs, are folded back on both sides toward the folded edge and the overlapping portions of these tabs are joined together.        A bottom patch is then attached, for example heat-sealed, to the folded bottom opening in the bottom patch station.        
The individual processing steps of the aforementioned processing stations are usually carried out on both ends of the tube piece. These processing stations are constructed identically on the operating and drive sides of the processing stations in the bag-making machines existing in reality.
It should be mentioned here that all the stations listed above need not be present in an apparatus for producing bags. It is thus possible to dispense with a pre-creasing station. It is also not required to always apply bottom patches in order to produce a bag. Nonetheless, the apparatus may also comprise additional processing stations.
A process of producing bags by the use of machines known in the prior art is explained in brief below. Since the machines known in the prior art are constructed almost identically on the operating and drive sides in order to enable the simultaneous processing of both ends of the tube piece, the different machine sides will not be explained in detail in the following description. A previously separated tube piece is guided along its longitudinal axis with the help of a suitable transport device (for example, a double belt conveyor) to a pre-creasing station. Here, a form punch is lowered onto the tube pieces in a direction extending at right angles to the transport direction of the tube pieces to form folded edges. The turned-in corners of the opened bag bottom, which is shaped in the subsequent bottom-opening station, will later be located on the resulting folded edges. A valve is later fitted to the open bottom in the valve patch station. This valve enables the bag to be filled later by means of a suitable filling device. In the subsequent closing station, the bottom opening of the bag is folded up so that the bag is then finished in the bottom patch station by heat-sealing the bottom opening of the bag to a bottom patch.
The disadvantage of the identical construction of the mutually opposing processing stations known in the prior art is that the tools of the processing stations obstruct each other in the case of small bag formats.
A further disadvantage of this construction of the mutually opposing processing stations consists in the maintenance of the same. When processing stations are located opposite to each other, the often large installation space thereof impedes their accessibility for maintenance purposes. Since a plurality of movable parts is located in the processing stations, it is sometimes necessary to also reset or readjust the same. As a result of the laterally reversed construction of the mutually opposing individual processing stations of the machine, the processing stations are accessible only with difficulty for purposes of altering settings and adjustments.